Question

我收到了以下oracle日志：

DEADLOCK DETECTED ( ORA-00060 )

[Transaction Deadlock]

The following deadlock is not an ORACLE error. It is a
deadlock due to user error in the design of an application
or from issuing incorrect ad-hoc SQL. The following
information may aid in determining the deadlock:

Deadlock graph:
                       ---------Blocker(s)--------  ---------Waiter(s)---------
Resource Name          process session holds waits  process session holds waits
TX-00120007-0002acbf        82     185     X             67     240           X
TX-0008001c-0009ed94        67     240     X             82     185           X

session 185: DID 0001-0052-00000004 session 240: DID 0001-0043-00000004 
session 240: DID 0001-0043-00000004 session 185: DID 0001-0052-00000004 

Rows waited on:
  Session 185: obj - rowid = 0001285C - AAAShcAAiAAEoVFAAi
  (dictionary objn - 75868, file - 34, block - 1213765, slot - 34)
  Session 240: obj - rowid = 0001285C - AAAShcAAiAAEoRWAA3
  (dictionary objn - 75868, file - 34, block - 1213526, slot - 55)

----- Information for the OTHER waiting sessions -----
Session 240:
  sid: 240 ser: 7 audsid: 32762787 user: 76/NETCRACKER1
    flags: (0x8000041) USR/- flags_idl: (0x1) BSY/-/-/-/-/-
    flags2: (0x40008) -/-
  pid: 67 O/S info: user: oracle, term: UNKNOWN, ospid: 26869908
    image: oracle@opipodb1
  client details:
    O/S info: user: adipoas1, term: unknown, ospid: 1234
    machine: opipoas1 program: JDBC Thin Client
    application name: JDBC Thin Client, hash value=2546894660
  current SQL:
  select o.object_id
  from nc_objects o,
       (select object_id
          from nc_objects
        connect by prior object_id = parent_id
         start with object_id = :a1
        union
        select object_id
          from nc_references
         where reference in (select object_id
                               from nc_objects
                             connect by prior object_id = parent_id
                              start with object_id = :a1)) ids
 where o.object_id = ids.object_id
 order by o.object_id
   for update of o.object_id

----- End of information for the OTHER waiting sessions -----

Information for THIS session:

----- Current SQL Statement for this session (sql_id=3mxkkzhttwa2q) -----
select o.object_id
  from nc_objects o,
       (select object_id
          from nc_objects
        connect by prior object_id = parent_id
         start with object_id = :a1
        union
        select object_id
          from nc_references
         where reference in (select object_id
                               from nc_objects
                             connect by prior object_id = parent_id
                              start with object_id = :a1)) ids
 where o.object_id = ids.object_id
 order by o.object_id
   for update of o.object_id
===================================================

是否意味着两个相等的查询（但可能有不同的数据）相互锁定？

如果是这样，怎么会发生？ - 这个查询锁定有序序列，我想我们不能在这里遇到死锁。

DB是元模型 object_id - PK

由于

Answer 1

ORDER BY will not always prevent deadlocks

这是一种可能导致查询死锁的情况：

会话1使用:id=A
会话2使用:id=B
会话1使用:id=B运行您的查询，会话1现在正在等待会话2
会话2使用:id=A运行您的查询，发出死锁

当您发出SELECT FOR UPDATE时，您将面临等待其他会话的风险。如果此会话已在等待您，则会出现死锁。

避免OLTP环境中死锁的一种常见方法是仅发出SELECT FOR UPDATE NOWAIT。让第二个会话失败而不是等待。

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您有多个会话更新同一个表。你有可能互相阻挡。如果你让他们等待并且他们更新了多行，你就有机会陷入僵局。您有很多选择来管理它：

让会话陷入僵局。 Oracle将自动检测到这一点并回滚一个。 Oracle will only rollback the last statement of one of the session, not the whole transaction，这意味着获取错误的会话应先回滚，然后再重试。
按照我的建议，用NOWAIT运行它们。
如果您不想让它们失败，您可以：
1. 使用NOWAIT锁定行
2. 如果ORA-56 回滚
3. 睡眠后从事务开始重试（X秒）。
4. 序列化更新。这通常通过确保只有一个会话可以同时更新表（或一系列行）来完成。
  例如，您可以让所有会话INSERT在事务表中，并让单个作业将修改合并到最终表中。并发会话无法阻止彼此。这显然会将更新推迟到主表（至少在提交之后）。

Oracle为更新DeadLock选择订单

1 个答案:

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